1. Field of the Invention
The present invention relates to a sheet feed device for feeding a recording sheet in cut form, such as sheets of paper, to an image transferring station or a printing station in a recording machine. The invention also relates to a sheet feed device wherein stacked recording sheets of different types, such as different sizes and sheet quality, are held in corresponding cassettes and fed selectively one sheet at a time to an image transferring or a printing station.
2. Description of the Related Art
A typical example of a recording machine to which the present invention relates is a laser electrophotographic recording machine. In such a recording machine, a photoconductive medium formed on a surface of a drum is charged to a substantially uniform potential to sensitize the surface thereof. The charged portion of the photoconductive surface is exposed to a light image of an original document to be reproduced. This records an electrostatic latent image on the photoconductive medium corresponding to the information areas contained within the original document. Thereafter, the latent image is developed by bringing a developer material into contact therewith. This forms a toner powder image on the photoconductive medium which is subsequently transferred to a recording sheet. Finally, the recording sheet is heated to permanently affix the toner powder image on the recording sheet.
Generally, the recording sheet used in the recording machine is of a ribbon-like continuous sheet type of a single size, or a cut sheet type having various sizes. In the present invention, the recording sheet of cut sheet type is used, and hereinafter, is simply referred to as a sheet. The sheets of one type in size and quality are held stacked in alignment in one cassette-like sheet holding means (hereinafter referred to as a cassette). Usually, a plurality of cassettes are stacked one above another, forwardly projectable in or from supporting means such as shelves or rails fixed to a frame. Each cassette has a signal actuator for signifying the sheet type for the sheets held therein.
FIG. 1 and FIG. 2 are schematic diagrams illustrating the arrangement of known sheet feed devices. In the apparatus of FIG. 1 cassettes 101 and 102 are disposed forwardly projecting out of an apparatus housing 103, thus occupying floor space in the office when installed. A sheet delivered from the cassette 101 is fed through a transfer passage 104, and a sheet delivered from the cassette 102 is fed through a feed passage 105. Both sheets are fed to an image transfer station 109 in succession where a toner image formed on a photoconductive drum 106 is transferred onto the sheets by an image transfer member 107. Thereafter, each sheet is fed through a passage 110 (shown by an arrow) to an image fixer 108 for fixing the transferred image on the sheets. The surface of the drum 106 is electrically discharged and cleaned by a discharger (not shown) after image transfer is completed.
In the apparatus of FIG. 2, cassettes 111 and 112 are stacked one above another at a lower portion of a housing 113 of the recording machine. A sheet delivered from the cassette 111 is fed through a feed passage 114, and a sheet delivered from a cassette 112 is fed through a feed passage 115. Through a pair of drive rollers 125 and a conveying passage 122, both sheets are respectively conveyed to an image transfer station 119 where a toner image formed on a photoconductive drum 116 is transferred onto the sheet by an image transfer member 117. Thereafter, the sheet is fed through the conveying passage 122 (indicated by an arrow) to an image fixer 118 for fixing the transferred image.
A manual feed passage 123 is disposed through the wall at the side F of the housing 113, facing the feed rollers 125. The surface of the drum 116 is electrically discharged and cleaned by a discharger (not shown) after image transfer is completed. A rectangular structure 120, shown by broken lines, represents a converging mechanism wherein the two feed passages 114 and 115 are joined to a common transfer passage 121 through which the sheets are delivered from the cassettes 111 and 112 to the conveying passage 122. Naturally, the rectangular structure 120 prohibits loading and unloading of the cassettes 111 and 112 from the side F of the housing 113. Thus, loading and unloading operations must be performed from the opposite side B. If a sheet is fed manually through the manual feed passage 123 and becomes jammed in the cassettes 111 or 122, the jammed sheet or sheets must be removed by opening various portions of the housing 113. This is because sheet jamming tends to occur in the vicinity of a portion of the relevant cassette where a sheet is delivered from the cassette (namely from the side F). The operation to remove a jammed sheet and resume the recording operation is not easy and is usually a time consuming matter. In order to perform the manual sheet feed operation and the jammed sheet removal operation, an additional area of floor space is required for an operator in front of the side F. Thus, two areas of floor space for operation at both sides F and B of the housing 113 must be maintained in the office, thereby restricting freedom of placement of the apparatus in the office. Moreover, the rectangular structure 120 provides the recording apparatus with an adverse effect on space-saving in an office, which is an important characteristic of an office machine. A need exists to reduce restrictions on the operating side for loading and unloading sheets to or from the cassettes.
Another problem associated with known recording apparatuses relates to the indicators used to indicate the sheet type of a particular cassette. For instance, in a known sheet feed means, an actuator of a fixed type indicates only for a single sheet type which is peculiar to the cassette. As the result, a cassette specified to receive sheets of a particular type cannot be used as a cassette for receiving sheets of a different sheet type. To enhance the freedom of use of the cassettes, it would be desirable to have the actuator manually changed by an operator or automatically changed by a controller of the apparatus to meet the requirements of each use.